The present invention relates generally to mass flow metering, and more particularly to a conveyor system for using gravimetric metering to control mass flow.
Conveyor belts are used in a variety of applications to transport bulk solid material. Most processing systems using conveyor belts monitor or meter mass flow in some way. Such systems typically estimate mass flow volumetrically, by multiplying a monitored and controlled belt speed by a fixed estimate of linear material density (e.g. kg/m). Such estimates assume that mass flow is dependent only on belt speed, and ignore variations in belt coverage (i.e. variations in width and depth of material on the conveyor belt), material density (e.g. kg/m3), and transport speed (e.g. due to blockage of the belt). For many applications these assumptions are unproblematic. In some other applications, however, the belt coverage, density, and transport speed of material on a conveyor belt can vary considerably during ordinary system operation. In asphalt processing, for example, the density of recycled asphalt shingles to be incorporated into new asphalt production can vary by 15% or more over the contents of a single bin, and bridging can cause partial or even complete obstructions that block material flow despite belt movement. In agricultural applications, similarly, grain and other unprocessed agricultural products can vary in density depending on material size, shape, and packing. There is a need for a mass flow metering system that can compensate for the inaccuracies of purely volumetric metering of such materials, for mechanical problems such as material flow cavitation and bin discharge bridging, and for human error such as bins being allowed to go empty.